The more general reactions of the cardiovascular system of man to the inhalation of oxygen-poor gas mixtures have been described by numerous investigators.1 They consist of an almost immediate increase in the heart rate, a slight rise in the systolic blood pressure, with no significant change in the diastolic level, and a definite augmentation in the cardiac output. With respect to alterations in the peripheral circulation, the results are not as clearcut. Freeman and his associates2 studied the rate at which blood flows through the hand during a period of acute anoxia, using the venous occlusion plethysmographic method. They found that either an increase or a decrease of rate was produced. Gellhorn and Steck,3 utilizing the same procedure and the same vascular bed, also noted apparently inconsistent results, the flow being decreased, unchanged or slightly increased.
Since the circulation through the hand is affected by a variety